Rotary shafts are often supported in a bearing housing by two bearings. Lubricating oil for the bearings can be supplied to a supply opening in a central channel formed as a pocket bore through one end face of the shaft. Radial bores (oil exit openings) are provided through the end of the central channel, and oil proceeds through these openings and into the bearing as a consequence of centrifugal forces due to rotation of the shaft. The central channel therefore extends from the supply opening in the shaft end face at least up to the bearing most remote from the supply opening. As a rule, shafts of this type are operated while vertically oriented. The supply opening is situated at the lower end of the shaft. In some instances, oil is supplied to the central channel through the supply opening by means of an oil sump. The upper bearing of such an arrangement particularly is jeopardized by descending dirt particles.
The employment of shafts of the described type is known, for example, in turbomolecular vacuum pumps. Turbomolecular vacuum pumps are operated at extremely high speeds (40,000 revolutions per minute and more). The stresses inherent in such an extreme environment place stringent demands on the lubrication system for oil bearings. First, dirt particles must be prevented from entering into the oil stream; second, the quantity of oil supplied to the bearings must be exactly metered. In most existing systems, the quantity of oil conveyed through the central channel in the shaft to the oil exit opening is usually too great.